Generally, electrode material for use in an electroluminescent device is formed on an entire substrate in the form of a thin film, and then patterned in a particular configuration depending on an object of a process.
Conventional methods of manufacturing electrodes for use in a flat display device include a method of putting a mask above a substrate and forming a thin film only on exposed portions of the substrate, and a method of forming a thin film of electrode on the entire substrate and then etching unnecessary portions of the thin film of electrode.
Particularly, the latter method is primarily used for indium-tin-oxide (In2O3:Sn, ITO) containing zinc oxide which is employed in the electroluminescent device. and the ITO is etched in a line or particular configuration.
In a case where the electrodes are formed in the above conventional configuration, a process of manufacturing the electrodes is as follows:
That is, the process comprises the steps of cleaning a substrate; forming a thin film of electrode on the entire substrate; coating photoresist on the thin film of electrode; putting a mask with patterns above the photoresist, exposing the masked surface of the substrate to light and developing the exposed surface; removing unnecessary portions of the photoresist and etching unnecessary portions of the thin film of electrode; and removing the remaining portions of the photoresist and cleaning the substrate.
Accordingly, as shown in FIG. 1, conventional electrodes 2 formed on the substrate 1 protrude therefrom. Since a thin film formed on the electrodes is processed depending on the configuration of the electrodes, the thin film protrudes at portions where the electrodes 2 remain and is depressed at portions where the electrodes 2 have been etched.
When additional electrodes having the opposite polarity are formed in a rugged profile on this thin film, non-uniformity of the thin film and concentration of an electric field on edge portions of the electrodes cause the electric field to be unevenly distributed between the electrodes.
Such a problem causes leakage current between the electrodes, thereby leading to various problems such as non-uniform luminescent characteristics between pixels or a low efficiency of the device.
Moreover, when the thickness of the electrodes formed on the substrate is reduced to alleviate the above problems, the resistance of the electrodes themselves is increased, and thus, voltage drop is produced within the electrodes.
Particularly, there is a problem in that the voltage drop produced within the electrodes limits the operation of the display device when the display device becomes larger in size.
Further, line widths of the electrodes are reduced in a case where the size of pixels is reduced, for example, in case of a micro display device. Therefore, according to the conventional methods, there are disadvantages in that it is difficult to implement the device due to the voltage drop produced within the electrodes, and there are also numerous difficulties in manufacturing the device.